A CONTROLLED ENVIRONMENT CHAMBER FOR GROWING PLANTS ACROSS A SUBAMBIENT CO2 GRADIENT

1. An elongated, controlled environment chamber is described in which a continuous, reproducible gradient of subambient CO2 Concentration ([CO2]) is maintained during daylight hours to assess plant responses to past increases in atmospheric [CO2]. 2. The [CO2] of air moved unidirectionally through the 37-6-m long chamber by a blower is progressively depleted by photosynthesis of plants growing in the chamber. 3. Plant top-growth is contained in a transparent film tunnel which rests upon an enclosed soil volume that is 45 cm wide and 76 cm deep. 4. The desired minimum concentration to which CO2 is depleted at the end of the chamber, usually 150 or 200 mul l-1, is maintained by varying the blower speed with a micrologger program dependent upon real-time sensing Of [CO2] and light intensity. 5. Dewpoint and dry bulb temperatures are also controlled by a micrologger- and computer-monitored air-conditioning system.